U.S. patent number 5,838,526 [Application Number 08/852,512] was granted by the patent office on 1998-11-17 for load actuation circuit with a surge protecting function.
This patent grant is currently assigned to Anden Co. Ltd, Denso Corporation. Invention is credited to Hiroyuki Ban, Fukuo Ishikawa, Masahisa Makino, Akira Sugiura.
United States Patent |
5,838,526 |
Ishikawa , et al. |
November 17, 1998 |
Load actuation circuit with a surge protecting function
Abstract
In a load actuation circuit of an emitter-follower circuit
arrangement, a surge detection circuit detects a power surge
voltage superposed on a power voltage of a power line. A feed
circuit supplies current to a control electrode of an output
transistor (i.e. emitter-follower transistor) from the power line
to turn on the output transistor forcibly when any power surge
voltage is detected by the surge detection circuit. Thus, the power
surge voltage is absorbed by the output transistor.
Inventors: |
Ishikawa; Fukuo (Kariya,
JP), Sugiura; Akira (Okazaki, JP), Makino;
Masahisa (Oobu, JP), Ban; Hiroyuki (Aichi-ken,
JP) |
Assignee: |
Anden Co. Ltd (Anjo,
JP)
Denso Corporation (Kariya, JP)
|
Family
ID: |
14585693 |
Appl.
No.: |
08/852,512 |
Filed: |
May 7, 1997 |
Foreign Application Priority Data
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May 7, 1996 [JP] |
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8-112399 |
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Current U.S.
Class: |
361/118; 361/56;
361/111; 361/115 |
Current CPC
Class: |
H03K
17/0826 (20130101); H03K 2217/0036 (20130101) |
Current International
Class: |
H03K
17/082 (20060101); H03K 17/00 (20060101); H02H
009/00 () |
Field of
Search: |
;361/91,93,115,56,111,113,100,118 |
References Cited
[Referenced By]
U.S. Patent Documents
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5444595 |
August 1995 |
Ishikawa et al. |
5465190 |
November 1995 |
Meunier et al. |
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Foreign Patent Documents
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50-036942 |
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Apr 1975 |
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JP |
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62-090717 |
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Apr 1987 |
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JP |
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62-152331 |
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Jul 1987 |
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JP |
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Primary Examiner: Gaffin; Jeffrey A.
Assistant Examiner: Jackson; Stephen
Attorney, Agent or Firm: Pillsbury Madison & Sutro
Claims
What is claimed is:
1. A load actuation circuit with a surge protection function
comprising:
an output transistor having a collector receiving a power voltage
from a power line, an emitter connected to one end of a load that
is grounded at the other end, and a control electrode;
a control circuit for controlling an electric potential of said
control electrode of said output transistor to turn on or off said
output transistor;
a surge detection circuit connected between said power line and a
ground line in parallel with said output transistor for detecting a
power surge voltage superposed on said power voltage of said power
line, said surge detection circuit including a constant-voltage
diode; and
a feed circuit responsive to a surge detection voltage of said
surge detection circuit for supplying a current to said control
electrode of said output transistor from said power line to turn on
said output transistor when any power surge voltage is detected by
said surge detection circuit, said feed circuit causing a voltage
drop between said collector and said control electrode of said
output transistor when said output transistor is turned on in
response to said surge detection voltage of said surge detection
circuit, said voltage drop at said output transistor being smaller
than a voltage drop at said constant-voltage diode of said surge
detection circuit.
2. The load actuation circuit with a surge protection function in
accordance with claim 1, wherein said surge detection circuit
comprises a resistance element connected in series with said
constant-voltage diode between said power line and a ground line,
and said power surge voltage is detected by a voltage drop at said
resistance element.
3. The load actuation circuit with a surge protection function in
accordance with claim 1, wherein the collector of said output
transistor is connected to the power line via a resistant
element.
4. The load actuation circuit with a surge protection function in
accordance with claim 1, further comprising a junction diode
serially connected between an output terminal of said control
circuit and said control electrode of said output transistor for
preventing a backward current from flowing from said control
electrode to said output terminal.
5. The load actuation circuit with a surge protection function in
accordance with claim 1, wherein said control circuit has an output
terminal grounded only through said load.
6. A load actuation circuit with a surge protection function
comprising:
an output transistor having a collector receiving a power voltage
from a power line and an emitter connected to one end of a load
that is grounded at the other end;
a control circuit for controlling an electric potential of a
control electrode of said output transistor to turn on or off said
output transistor;
a surge detection circuit for detecting power surge voltage
superposed on said power voltage of said power line; and
a feed circuit responsive to a surge detection voltage of said
surge detection circuit for supplying a current to said control
electrode of said output transistor from said power line to turn on
said output transistor when any power surge voltage is detected by
said surge detection circuit, wherein
said surge detection circuit comprises a constant-voltage diode and
a resistance element connected in series between said power line
and a ground line, and said power surge voltage is detected by a
voltage drop at said resistance element,
said constant-voltage diode of said surge detection circuit has a
cathode connected to said power line;
a lower potential terminal of said resistance element of said surge
detection circuit is connected to the ground line;
said feed circuit comprises an inversion circuit and an activation
control section;
said inversion circuit is turned on in response to said surge
detection voltage produced from said surge detection circuit and
generates a low-level potential; and
said activation control circuit is turned on in response to the
low-level potential of said inversion circuit and supplies electric
power from said power line to said control electrode of said output
transistor.
7. A load actuation circuit with a surge protection function
comprising:
an output transistor having a collector receiving a power voltage
from a power line and an emitter connected to one end of a load
that is grounded at the other end;
a control circuit for controlling an electric potential of a
control electrode of said output transistor to turn on or off said
output transistor;
a surge detection circuit for detecting a power surge voltage
superposed on said power voltage of said power line; and
a feed circuit responsive to a surge detection voltage of said
surge detection circuit for supplying a current to said control
electrode of said output transistor from said power line to turn on
said output transistor when any power surge voltage is detected by
said surge detection circuit, wherein
said surge detection circuit comprises a constant-voltage diode and
a resistance element connected in series between said power line
and a ground line, and said power surge voltage is detected by a
voltage drop at said resistance element,
said constant-voltage diode of said surge detection circuit has an
anode connected to said ground line;
a higher-potential terminal of said resistance element of said
surge detection circuit is connected to the power line; and
said feed circuit comprises a transistor turned on in response to
said surge detection voltage produced from said surge detection
circuit and supplies a high-level potential to said control
electrode of said output transistor.
8. A load actuation circuit with a surge protection function
comprising:
an output transistor having a collector receiving a power voltage
from a power line and an emitter connected to one end of a load
that is grounded at the other end, and a control electrode;
a control circuit controlling an electric potential of said control
electrode of said output transistor to turn on or off said output
transistor;
a feed circuit supplying current to said control electrode of said
output transistor from said power line to turn on said output
transistor when any power surge voltage is superposed on the power
voltage of said power line; and
a junction diode serially connected between an output terminal of
said control circuit and said control electrode of said output
transistor for preventing a backward current from flowing from said
control electrode to said output terminal.
9. The load actuation circuit with a surge protection function in
accordance with claim 8, wherein said feed circuit comprises a
constant-voltage diode and a current-limiting resistant element
serially connected between said power line and said control
electrode of said output transistor.
10. A load actuation circuit with a surge protection function
comprising:
an actuating transistor having one output terminal connected to a
power line and the other output terminal grounded via a load;
an actuating circuit producing a control signal that is supplied to
a control terminal of said actuating transistor to turn on said
actuating transistor;
a surge detection circuit connected between said power line and a
ground line in parallel with said actuating transistor for
detecting a surge voltage superposed on a power voltage of said
power line, said surge detecting circuit including a
constant-voltage diode; and
a surge actuating transistor responsive to a surge detection
voltage of said surge detection circuit and supplying an actuation
signal to said control terminal of said actuating transistor to
turn on said actuating transistor forcibly irrespective of said
control signal produced from said actuating circuit, said surge
actuating transistor having one output terminal connected to said
power source and the other terminal connected to said control
terminal of said actuating transistor, said surge actuating
transistor causing a voltage drop between said power line and said
control terminal of said actuating transistor when said actuating
transistor is turned on in response to said surge detection voltage
of said surge detection circuit, said voltage drop at said
actuating transistor being smaller than a voltage drop at said
constant-voltage diode of said surge detecting circuit.
11. The load actuation circuit with a surge protection function in
accordance with claim 10, wherein said one output terminal of said
actuating transistor is connected to the power line via a resistant
element.
12. The load actuation circuit with a surge protection function in
accordance with claim 10, further comprising a junction diode
serially connected between an output terminal of said actuating
circuit and said control terminal of said actuating transistor for
preventing a backward current from flowing from said control
terminal to said output terminal.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention:
This invention relates to a load actuation circuit, and more
particularly to an improvement of a transistor protecting function
of the load actuation circuit having an emitter-follower circuit
arrangement.
2. Related Art:
Laid-open Japanese Patent Application No. 50-36942, published in
1975, discloses a protection circuit protecting a transistor (i.e.,
a driver element) actuating a load against an excessive voltage
(i.e., a power surge voltage) superposed on a power voltage.
According to this protection circuit, a constant-voltage diode
(hereinafter, referred to as Zener diode) and a current-limiting
resistor are connected in series to constitute a surge responsive
circuit. This surge responsive circuit is interposed between a
control terminal of the driver element and a high-potential power
line. The surge responsive circuit turns on the driver element only
when the power voltage exceeds a breakdown voltage of the Zener
diode.
In short, this protection circuit supplies current to the base of
an emitter grounded transistor acting as the driver element via the
Zener diode and the current-limiting resistor in response to a
superposed power surge voltage. The driver element, turned on by
this current supply, absorbs and eliminates the power surge
voltage.
In some cases, an output transistor may be incorporated in an
emitter-follower circuit that is characterized by a collector
receiving electric power from a power line and an emitter grounded
via a load.
However, the above-described conventional protection circuit cannot
be directly applied to this kind of output transistor of an
emitter-follower circuit arrangement for the reasons described
below.
In combining the above-described conventional protection circuit
with an emitter-follower circuit, the surge sensitive circuit
(i.e., a serial arrangement of a Zener diode and a current-limiting
resistor) is connected between the base and collector of an
emitter-follower transistor. A power surge voltage (i.e. positive
surge) may be produced with a magnitude large enough to cause a
breakdown of the Zener diode. In this case, even if current is
supplied to the base of the emitter-follower transistor, the
base-collector voltage of the emitter-follower transistor becomes
larger than a breakdown voltage of the Zener diode by an amount
equivalent to a voltage drop at the current-limiting resistor.
As a result, a large collector loss (=collector
current.times.base-collector voltage) is generated. There is a
possibility that a power surge voltage may last for a long
duration. In view of the above, the durability of the output
transistor (i.e., emitter-follower transistor) needs to be grate
enough to endure the above-described collector loss. Thus, the
overall size of the output transistor becomes large.
In this respect, a conventional emitter-grounded transistor
receives a base current supplied to its base via the surge
responsive circuit in response to a power surge voltage, and is
turned on by this base current. In this case, the collector
potential of the conventional emitter-grounded transistor becomes a
grounded potential. Thus, the problems relating to collector loss
increase and heat generation will not be caused.
To supply a sufficient collector current Ic to an emitter-follower
transistor, it is necessary to increase its base potential
sufficiently by an amount equivalent to the sum of (load impedance
Z.times.collector current Ic+base-emitter on voltage Vbe). This
requires a large base charge current flowing across the surge
responsive circuit. A post-stage control circuit is provided for
controlling the emitter-follow transistor. An output terminal of
the post-stage control circuit is maintained at a low level, when
the emitter-follow transistor is turned off. Current is supplied
from the surge responsive circuit to the base of the
emitter-follower transistor (or a gate of IGBT An). This current is
absorbed by the control circuit. This is undesirable in that the
power surge voltage cannot be absorbed sufficiently, because the
turning-on of the emitter-follower transistor is delayed and the
current absorbing amount is limited significantly.
Furthermore, the power surge voltage applied from the surge
responsive circuit to the base of the emitter-follower transistor
may enter into the control circuit via its output terminal. This
will result in a breakdown of an output transistor or various
transistors at their PN junctions involved in the control circuit.
For this reason, the above-described conventional art requires
enhancement of the durability of elements constituting the control
circuit.
Still further, an emitter-follower transistor may be used to
control a large reactance load. In such a case, at a moment when
the emitter-follower transistor is turned off, its base potential
is quickly reduced to a negative voltage due to a large reverse
electromotive voltage of the reactance load. Therefore, the
withstanding voltage for the base-collector terminals of the
emitter-follower transistor needs to be increased to endure such a
negative voltage. This is not desirable in that improving the
collector withstanding voltage of an output transistor necessitates
a modification of its manufacturing process and increases the
collector loss.
SUMMARY OF THE INVENTION
An object of the present invention is to solve the above-described
problems. More specifically, an object of the present invention is
to improve the durability against any surge voltage in a load
actuation circuit having an emitter-follower transistor as an
output transistor.
An object of the present invention is to provide a load actuation
circuit capable of effectively absorbing a power surge voltage
superposed on the electric power.
An object of the present invention is to provide a system robust
against a power surge voltage even if the power surge voltage is
applied to the output terminal of a control circuit of the load
actuation circuit.
An object of the present invention is to reduce the power
consumption in the load actuation circuit.
An object of the present invention is to reduce the collector loss
in the output transistor of an emitter-follower type when a power
surge voltage is absorbed.
An object of the present invention is to provide a load actuation
circuit capable of surely preventing any backward current flowing
from the control electrode of the output transistor to the output
terminal of the control circuit.
An object of the present invention is to provide a load actuation
circuit capable of quickly increasing the electric potential of the
control electrode of the output transistor.
An object of the present invention is to provide a load actuation
circuit capable of realizing a speedy absorption of a power surge
voltage by the output transistor.
An object of the present invention is to provide a load actuation
circuit capable of surely protecting a delicate junction of an
internal transistor in the control circuit against a power surge
voltage.
Still another object of the present invention is to provide a load
actuation circuit capable of surely protecting the output
transistor against a negative surge voltage without increasing the
withstanding voltage of this output transistor.
In order to accomplish above-described and other related objects,
the present invention provides a novel and excellent load actuation
circuit having various aspects which will be described hereinafter
with reference to numerals in parentheses which show the
correspondence to the components described in preferred embodiments
of the present invention described later. Reference numerals in
parentheses, added in the following description, are merely used
for the purpose of helping the understanding to the present
invention and not used for narrowly interpreting the scope of
claims of the present invention.
More specifically, a first aspect of the present invention provides
a load actuating circuit with a surge protection function
characterized by the following features.
An output transistor (T1) has a collector receiving a power voltage
from a power line (200) and an emitter connected to one end of a
load (202) that is grounded at the other end. A control circuit
(103) controls an electric potential of a control electrode of the
output transistor (T1) to turn on or off the output transistor
(T1). A surge detection circuit (101) detects a power surge voltage
superposed on the power voltage of the power line (200). And, a
feed circuit (104), responsive to a surge detection voltage of the
surge detection circuit (101), supplies current to the control
electrode of the output transistor (T1) from the power line (200)
to turn on the output transistor (T1) when any power surge voltage
is detected by the surge detection circuit (101).
Preferably, the surge detection circuit (101) comprises a
constant-voltage diode (D3, D4, D5) and at least one resistance
element (R11, R12; R21) connected in series between the power line
(200) and a ground line (201). The power surge voltage is detected
by a voltage drop at the resistance element (R11, R12).
In more detail, the constant-voltage diode (D3) of the surge
detection circuit (101) has a cathode connected to the power line
(200). A lower-potential terminal of the resistance element (R12)
of the surge detection circuit (101) is connected to the ground
line (201). The feed circuit (104) comprises an inversion circuit
(T3, R3, R4) and an activation control section (T2). The inversion
circuit (T3, R3, R4) is turned on in response to the surge
detection voltage produced from the surge detection circuit (101)
and generates a low-level potential. And, the activation control
circuit (T2) is turned on in response to the low-level potential of
the inversion circuit (T3, R3, R4) and supplies electric power from
the power line (200) to the control electrode of the output
transistor (T1).
According to another embodiment the constant-voltage diode (D5) of
the surge detection circuit (101) has an anode connected to the
ground line (201). A higher-potential terminal of the resistance
element (R21) of the surge detection circuit (101) is connected to
the power line (200). The feed circuit (104) comprises a transistor
(T2) turned on in response to the surge detection voltage produced
from the surge detection circuit (101) and supplies a high-level
potential to the control electrode of the output transistor
(T1).
Preferably, the collector of the output transistor (T1) is
connected to the power line (200) via a resistant element (R1).
Preferably, the load actuation circuit further comprises a junction
diode (D2) preventing flow of backward current from the control
electrode of the output transistor (T1) to an output terminal of
the control circuit (103).
Furthermore, the control circuit (103) has an output terminal
grounded only through the load (202).
A second aspect of the present invention provides a load actuation
circuit with a surge protection function characterized by the
following features.
An output transistor (T1) has a collector receiving a power voltage
from a power line (200) and an emitter connected to one end of a
load (202) that is grounded at the other end. A control circuit
(103) controls an electric potential of a control electrode of the
output transistor (T1) to turn on or off the output transistor
(T1). A feed circuit (104) supplies current to the control
electrode of the output transistor (T1) from the power line (200)
to turn on the output transistor (T1) when any power surge voltage
is superposed on the power voltage of the power line (200). And, a
junction diode (D2) prevents flow of backward current from the
control electrode of the output transistor (T1) to an output
terminal of the control circuit (103).
Preferably, the feed circuit (104) of the second aspect load
actuation circuit comprises a constant-voltage diode (D6, D7, D8)
and a current-limiting resistant element (R31) serially connected
between the power line (200) and the control electrode of the
output transistor (T1).
A third aspect of the present invention provides a load actuation
circuit with a surge protection function characterized by the
following features.
An output transistor (T1) has a collector receiving a power voltage
from a power line (200) and an emitter connected to one end of a
load (202) that is grounded at the other end. A control circuit
(103) controls an electric potential of a control electrode of the
output transistor (T1) to turn on or off the output transistor
(T1). A feed circuit (104) supplies current to the control
electrode of the output transistor (T1) from the power line (200)
to turn on the output transistor (T1) when any power surge voltage
is superposed on the power voltage of the power line (200). And,
the control circuit (103) has an output terminal grounded only
through the load (202).
A fourth aspect of the present invention provides a load actuation
circuit with a surge protection function characterized by the
following features.
An output transistor (T1) has a collector receiving a power voltage
from a power line (200) and an emitter connected to one end of a
reactance load (202) that is grounded at the other end. A control
circuit (103) controls a base potential of the output transistor
(T1) to turn on or off the output transistor (T1). And, a feed
circuit (105) supplies current to a base of the output transistor
(T1) from a ground line (201) when the base potential of the output
transistor (T1) falls below a ground potential by an amount
exceeding a collector-base withstanding voltage of the output
transistor (T1).
Preferably, the feed circuit (105) of the fourth aspect load
actuation circuit comprises a resistance element (R2) connecting
the base of the output transistor (T1) to the ground line (201),
and a junction diode (D1) connected in series with the resistance
element (R2) preventing current from flowing across the resistance
element (R2) in a direction from the base of the output transistor
(T1) to the ground line (201).
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other objects features and advantages of the present
invention will become more apparent from the following detailed
description which is to be read in conjunction with the
accompanying drawings, in which:
FIG. 1 is a circuit diagram showing a load actuation circuit in
accordance with a first embodiment of the present invention;
FIG. 2 is a circuit diagram showing a load actuation circuit in
accordance with a second embodiment of the present invention;
FIG. 3 is a circuit diagram showing a load actuation circuit in
accordance with a third embodiment of the present invention;
FIG. 4 is a circuit diagram showing a load actuation circuit in
accordance with a fourth embodiment of the present invention;
and
FIG. 5 is a circuit diagram showing a load actuation circuit in
accordance with a fifth embodiment of the present invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
Preferred embodiments of the present invention will be explained
hereinafter with reference to accompanied drawings. Identical parts
are denoted by the same reference numerals throughout the
drawings.
First Embodiment
A load actuation circuit 100 comprises a surge detection circuit
101, an internal constant voltage circuit 102, a control circuit
103, a junction diode D2 having a function of preventing a backward
current, a first feed circuit 104, a second feed circuit 105, a
bypass resistor R5, and an output transistor T1.
A power line 200 extends from a high voltage terminal of a battery
B. The other terminal of the battery B is grounded via a ground
line 201.
The surge detection circuit 101 is interposed between the power
line 200 and the ground line 201. The surge detection circuit 101
comprises three Zener diodes (i.e., constant-voltage diodes) D3, D4
and D5 and two resistors R11 and R12 that are serially connected in
this order from the high voltage side to the ground potential side.
A cathode of Zener diode D3 is connected to the power line 200
(i.e., high voltage terminal of the battery B). The lower-potential
terminal of the resistor R12 is connected to the ground line
201.
The control circuit 103 comprises two transistors T5 and T4 and
resistors R6, R7, R8, R9 and R10.
The first feed circuit 104 comprises an NPN transistor T3, a PNP
transistor T2, a resistor R3 and a resistor R4. The NPN transistor
T3 has an emitter that is grounded. The PNP transistor T2 has an
emitter that is grounded. Resistors R3 and R4 are connected in
series so as to constitute a voltage dividing circuit. Furthermore,
resistors R3 and R4 serve as a load for transistor T3. The base of
transistor T2 is connected to an intermediate portion between
resistors R3 and R4. The emitter of transistor T2 is connected to
the power line 200. The collector of transistor T2 is connected to
the base (i.e., control electrode) of output transistor T1.
The second feed circuit 105 comprises resistor R2 and junction
diode D1 connected in series. The second feed circuit 105 is
interposed between the base of output transistor T1 and the ground
line 201.
The output transistor T1 is an emitter-follower transistor having a
collector connected to the power line 200 and an emitter grounded
via reactance load 202. The load actuation circuit 100 has
terminals D, S, E, V and L. Terminals D and V are connected to the
high voltage terminal of the battery B. Terminal E is connected to
the ground terminal of the battery B. An external switch SW is
provided between terminals D and S. And, the terminal L is
connected to the reactance load 202.
The operation of the above-described actuation circuit will be
explained.
When external switch SW is closed, the power voltage of power line
200 is applied to the resistors R9 and R10 serially connected. With
this application of power voltage, the NPN transistor T5 is turned
on. The NPN transistor T5, that has a grounded emitter arrangement,
is connected in parallel with the resistor R10. Resistors R7 and R8
serve as a load for transistor T5. Internal constant voltage
circuit 102 supplies collector current flowing into transistor T5
through resistors R7 and R8. The collector current causes a voltage
drop across resistor R7. In response to this voltage drop, the PNP
transistor T4 is turned on. The PNP transistor T4 has a grounded
emitter arrangement. Upon transistor T4 turning on, electric power
is supplied to the reactance load 202 via resistor R6, junction
diode D2 and resistor R6. A voltage drop is caused across resistor
R5. The magnitude of this voltage drop exceeds a predetermined
base-emitter ON voltage for output transistor T1 that is an
emitter-follower transistor. Thus, transistor T1 is turned on. In
other words, the collector current flows with an amount
proportional to the base current flowing between the base and the
emitter of transistor T1. In this manner, transistor T1 has a
function of feeding current to reactance load 202.
When the external switch SW is opened, transistors T5 and T4 are
turned off. Thus, no base current flows into the output transistor
T1. This quickly reduces both of the base potential and the emitter
potential of the output transistor T1. Especially, in the first
embodiment, the load 202 is a reactance load that causes a reverse
electromotive force and a negative surge voltage. Therefore, the
base potential and the emitter potential of the output transistor
T1 tend to have negative potentials due to such an abrupt
reduction.
The base potential reduction of the output transistor T1, entering
into a negative potential region, turns on the junction diode D1 of
the second feed circuit 105. Electric power is thus supplied to the
base of output transistor T1 via resistor R2 from the ground line
201. The resistor R2 has a function of limiting current flowing
across the junction diode D1. Hence, the potential reduction of the
base and the emitter of output transistor T1 is prevented. In other
words, the breakdown of the output transistor T1 at its
base-collector terminals is prevented effectively.
In short, the second feed circuit 105 supplies current to the base
of output transistor T1 from the ground line 201 in an event the
base potential of the output transistor T1 may fall below a ground
potential by an amount exceeding a collector-base withstanding
voltage of the output transistor T1.
As an extraordinary condition, there is a possibility that a power
surge voltage (i.e., a positive surge voltage) may be superposed on
the power voltage of the power line 200. An operation of the
above-described actuation circuit in such an extraordinary
condition will be explained hereinafter.
The power surge voltage superposed on the power line 200 may exceed
a breakdown threshold for Zener diodes D3, D4 and D5. As a result
of this nondestructive breakdown of Zener diodes D3, D4 and D5,
current flows across the voltage dividing circuit consisting of the
resistors R11 and R12 serially connected. An output of this voltage
dividing circuit, i.e., an intermediate potential between resistors
R11 and R12, is applied to the base of transistor T3 and the
transistor T3 is turned on.
Then, a voltage drop is caused at resistor R3 in accordance with
collector current flowing through transistor T3. This voltage drop
is applied to the base-emitter terminals of transistor T2, and the
transistor T2 is turned on. Then, electric power is supplied from
the power line 200 to the output transistor T1 via the
thus-activated transistor T2. The output transistor T1 is turned on
accordingly. In other words, the power surge voltage superposed on
power line 200 is absorbed by the output transistor T1 effectively
and is attenuated sufficiently.
The power surge voltage superposed on the power line 200 may
disappear. After that, Zener diodes D3, D4 and D5 of the surge
detection circuit 101 recover from the breakdown condition. In
response to the recovery of Zener diodes D3, D4 and D5, both of the
transistors T3 and T2 are turned off. Therefore, d.c. electric
power consumption is reduced effectively.
Furthermore, there is a possibility that the power surge voltage
superposed on the power line 200 may turn on the transistor T2. In
this case, the power surge voltage is applied to the base of output
transistor T1 via the transistor T2. On the other hand, the power
surge voltage increases a cathode potential Vk of the junction
diode D2. To prevent any adverse effect by the power surge voltage,
it is effective that the junction diode D2 has a breakdown voltage
high enough to endure such a surge voltage. For example, it is
preferable to constitute the junction diode D2 by a plurality of
junction diodes connected in series. As a result, an increase of
anode potential Va is prevented surely.
With this arrangement, it becomes possible to provide a system
robust against a power surge voltage. Even if the power surge
voltage is applied to the output terminal of the control circuit
103 via the transistor T2, it does not enter the inside of control
circuit 103 through the collector-base junction of its output
transistor T4. Thus, a collector potential Vc of the transistor T5
is not increased, and the collector-base junction of the transistor
T5 is not broken. Furthermore, an internal transistor (not shown)
incorporated in the internal constant voltage circuit 102 is not
broken. The resistors R5 and R6 have a function of adjusting the
base current for the output transistor T1.
According to the first embodiment, the transistors T2 and T3 of the
first feed circuit 104 (corresponding to a feed circuit of the
present invention) are turned off when the surge detection circuit
101 detects no power surge voltage. Therefore, d.c. electric power
can be saved effectively.
As described above, the first embodiment of the present invention
provides a load actuating circuit with a surge protection function
comprising: an output transistor (T1) having a collector receiving
a power voltage from a power line (200) and an emitter connected to
one end of a load (202) that is grounded at the other end; a
control circuit (103) controlling an electric potential of a
control electrode (i.e., gate) of the output transistor (T1) to
turn on or off the output transistor (T1); a surge detection
circuit (101) detecting a power surge voltage superposed on the
power voltage of the power line (200); and a feed circuit (104)
responsive to a surge detection voltage of the surge detection
circuit (101) for supplying current to the control electrode of the
output transistor (T1) from the power line (200) to turn on the
output transistor (T1) forcibly when any power surge voltage is
detected by the surge detection circuit (101), thereby effectively
absorbing the power surge voltage superposed on the electric
power.
According to the arrangement of the first embodiment, the feed
circuit (104) does not include any constant-voltage diode (i.e.,
Zener diode) equivalent to that shown in the conventional surge
sensitive circuit previously described. This is advantageous in
that the base-collector voltage of the emitter-follower transistor
can be reduced by an amount corresponding to a voltage drop at this
Zener diode. Furthermore, according to the arrangement of the first
embodiment, the base-collector terminals of the emitter-follower
transistor can be easily short-circuited. This is advantageous
compared with a conventional circuit in that the collector loss of
the emitter-follower transistor is remarkably reduced when a power
surge voltage is absorbed.
As the output transistor of the first embodiment, it is possible to
adopt a bipolar transistor or IGBT (i.e., insulated gate bipolar
transistor).
Preferably, the surge detection circuit (101) comprises a
constant-voltage diode (D3, D4, D5) and a resistance element (R11,
R12; R21) connected in series between the power line (200) and a
ground line (201). The power surge voltage is detected by a voltage
drop at the resistance element (R11, R12). Thus, the power surge
voltage can be detected quickly.
The resistance element for the first embodiment can be replaced by
any other element, such as a transistor, that has a tendency of
increasing its voltage drop in accordance with current flowing
therethrough.
In more detail, the constant-voltage diode (D3) of the surge
detection circuit (101) has a cathode connected to the power line
(200). A lower-potential terminal of the resistance element (R12)
of the surge detection circuit (101) is connected to the ground
line (201). The feed circuit (104) comprises an inversion circuit
(T3, R3, R4) and an activation control section (T2). The inversion
circuit (T3, R3, R4) is turned on in response to the surge
detection voltage produced from the surge detection circuit (101)
and generates a low-level potential. And, the activation control
circuit (T2) is turned on in response to the low-level potential of
the inversion circuit (T3, R3, R4) and supplies electric power from
the power line (200) to the control electrode of the output
transistor (T1).
This arrangement is advantageous in that the d.c. power consumption
of a transistor can be reduced to zero when the power surge voltage
is not produced. Furthermore, the power consumption can be reduced
significantly compared with a surge detecting method based on
resistance division.
Still further, the load actuation circuit of the first embodiment
comprises a junction diode (D2) preventing backward current flowing
from the control electrode of the output transistor (T1) to an
output terminal of the control circuit (103). This arrangement is
advantageous in the following reasons.
As a comparative circuit, there may be a control circuit that
absorbs current from the control electrode of an output transistor
when the output transistor is turned off. In such a control
circuit, the output transistor cannot be turned on quickly because
of the phenomenon that the control circuit absorbs the current from
the control electrode of the output transistor. And, the collector
loss is increased. However, according to the above-described first
embodiment, the junction diode (D2) surely prevents the backward
current flowing from the control electrode of the output transistor
(T1) to the output terminal of the control circuit (103).
Therefore, the electric potential of the control electrode of the
output transistor (T1) can be quickly increased. Thus, a speedy
absorption of the power surge voltage by the output transistor can
be realized.
Furthermore, the feed circuit (104) may apply a significant high
potential to the control electrode of the output transistor (T1)
due to the generation of a power surge voltage. Even in such a
case, the junction diode (D2) surely prevents such an extraordinary
potential from entering into the control circuit (103). Thus, the
delicate junction of an internal transistor in the control circuit
is surely protected against a power surge voltage.
Regarding the junction diode (D2) of this embodiment, it can be
constituted by a single junction diode or a plurality of junction
diodes.
Yet further, according to the arrangement of the first embodiment,
the control circuit (103) has an output terminal grounded only
through the load (202). In other words, the output stage of the
control circuit (103) has an open-emitter or open-collector
arrangement.
When any power surge voltage is generated, the feed circuit charges
the control electrode of the output transistor. The arrangement of
the first embodiment is advantageous in that, in this moment, the
current of the feed circuit does not flow partly into the control
circuit. Accordingly, the potential of the control electrode of the
output transistor can be increased quickly.
Furthermore, all of the current supplied from the feed circuit
entirely flows into the emitter of the output transistor via its
base. This is effective to improve the rate of increase of the
control electrode potential in the output transistor of an
emitter-follower transistor.
Still further, the first embodiment of the present invention
provides a load actuation circuit with a surge protection function
characterized by the following features. An output transistor (T1)
has a collector receiving a power voltage from a power line (200)
and an emitter connected to one end of a load (202) that is
grounded at the other end. A control circuit (103) controls an
electric potential of a control electrode of the output transistor
(T1) to turn on or off the output transistor (T1). A feed circuit
(104) supplies current to the control electrode of the output
transistor (T1) from the power line (200) to turn on the output
transistor (T1) forcibly when any power surge voltage is superposed
on the power voltage of the power line (200). The control circuit
(103) has an output terminal grounded only through the load (202).
Thus, any power surge voltage is effectively absorbed by the output
transistor.
Especially, according to the arrangement of the first embodiment,
the output terminal of the control circuit (103) is grounded only
through the load (202). In other words, the output stage of the
control circuit (103) is constituted by an open-collector or
open-emitter arrangement as described above. Thus, the
above-described effect can be obtained.
Yet further, the first embodiment of the present invention provides
a load actuation circuit with a surge protection function
characterized by the following features. An output transistor (T1)
has a collector receiving a power voltage from a power line (200)
and an emitter connected to one end of a reactance load (202) that
is grounded at the other end. A control circuit (103) controls a
base potential of the output transistor (T1) to turn on or off the
output transistor (T1). And, a feed circuit (105) supplies current
to a base of the output transistor (T1) from a ground line (201)
when the base potential of the output transistor (T1) falls below a
ground potential by an amount exceeding a collector-base
withstanding voltage of the output transistor (T1).
This arrangement is advantageous in that the output transistor (T1)
can be surely protected against a negative surge voltage without
increasing the base-collector withstanding voltage of the output
transistor.
Moreover, the feed circuit (105) comprises a resistance element
(R2) connecting the base of the output transistor (T1) to the
ground line (201), and a junction diode (D1) connected in series
with the resistant element (R2) to prevent current from flowing
across the resistant element (R2) in a direction from the base of
the output transistor (T1) to the ground line (201). Thus, the
circuit arrangement can be simplified.
Second Embodiment
A second embodiment will be explained with reference to FIG. 2. The
second embodiment is different from the first embodiment in that a
resistor R1 is provided between the high voltage terminal of the
battery B and the terminal V of the load actuation circuit 100. The
resistor R1 has a low resistance. According to the arrangement of
the second embodiment, electric power is supplied to the first feed
circuit 104 and the collector of output transistor T1 via the
resistor R1. This is effective to delay the arrival of any power
surge voltage to the output transistor T1 and suppress the wave
height of the power surge voltage. Accordingly, the protection
function of the output transistor T1 can be further improved.
As apparent from the foregoing description, the collector of the
output transistor (T1) is connected to the power line (200) via a
resistance element (R1). Thus, it becomes possible to attenuate any
power surge voltage applied to the collector. The output transistor
(T1) can be surely prevented from being damaged. The application
timing of the power surge voltage can be delayed adequately. Thus,
any delay in an ON operation of the output transistor can be
compensated.
Third Embodiment
A third embodiment will be explained with reference to FIG. 3. The
third embodiment is different from the first embodiment in the
arrangement of the surge detection circuit 101 and the arrangement
of the first feed circuit 104. More specifically, the surge
detection circuit 101 comprises Zener diodes D3, D4 and D5 serially
connected and disposed at its low-voltage side. An anode of the
lowermost Zener diode (i.e., constant-voltage diode) D5 is
connected to the ground line 201. A resistor R21 is connected in
series with these Zener diodes D3, D4 and D5 and disposed at the
high-voltage side of the surge detection circuit 101. A
high-potential terminal of the resistor R21 is connected to the
power line 200. The first feed circuit 104 is constituted by a
combination of a resistor R22 and the transistor T2. The resistor
R22 has a function of limiting the amount of current supplied to
the base of transistor T2.
In this case, it is possible to omit the resistor R22 and replace
the resistor R21 by the voltage dividing circuit (R11 and R12)
shown in FIG. 1.
An operation of the third embodiment will be explained below.
A power surge voltage may occur with a magnitude causing a
breakdown of Zener diodes D3, D4 and D5. In response to this
nondestructive breakdown of Zener diodes D3, D4 and D5, current
flows across the resistor R21 and the transistor T2 is turned on.
Then, electric power is supplied from the power line 200 to the
output transistor T1 via the thus-activated transistor T2. The
output transistor T1 is turned on accordingly. Thus, power surge
voltage superposed on power line 200 is absorbed by the output
transistor T1 effectively and is attenuated sufficiently.
The arrangement of the third embodiment has a small circuit delay.
Hence, the output transistor T1 can be activated quickly in
response to a power surge voltage.
Furthermore, the arrangement of the first feed circuit 104
consisting of resistor R22 and transistor T2 is advantageous in
that d.c. electric power consumption is small and the circuit
arrangement is simple.
As described above, according to the third embodiment of the
present invention, the constant-voltage diode (D5) of the surge
detection circuit (101) has an anode connected to the ground line
(201). A higher-potential terminal of the resistance element (R21)
of the surge detection circuit (101) is connected to the power line
(200). The feed circuit (104) comprises a transistor (T2) turned on
in response to the surge detection voltage produced from the surge
detection circuit (101) and supplies a high-level potential to the
control electrode of the output transistor (T1).
With this arrangement, it becomes possible to reduce the d.c. power
consumption of the transistor to zero when no power surge voltage
is generated. Furthermore, in the same manner in the first
embodiment, the power consumption can be reduced. Yet further,
according to the third embodiment, the feed circuit (104) has a
single-stage arrangement. This is advantageous in that the circuit
arrangement can be simplified and the on-delay time can be reduced.
Accordingly, the absorption of a power surge voltage can be quickly
accomplished.
Fourth Embodiment
A fourth embodiment will be explained with reference to FIG. 4. The
fourth embodiment is different from the second embodiment in that
the surge detection circuit 101 is omitted and the first feed
circuit 104 is constituted differently. More specifically, the
first feed circuit 104 is provided between the power line 200 and
the base of output transistor T1. The first feed circuit 104
comprises Zener diodes D6, D7 and D8 serially connected. A resistor
R31 is connected in series with these Zener diodes D6, D7 and D8.
The resistor R31 has a low resistance and acts as a means for
limiting current flowing through the Zener diodes D6, D7 and
D8.
Furthermore, an NMOS transistor T7 is provided with one end
connected to an intermediate point between resistor R6 and junction
diode D2 and the other end connected to ground. This NMOS
transistor T7 has a source grounded, a drain connected to an anode
of the junction diode D2, and a gate connected to the collector of
transistor T5.
When a power surge voltage superposed on the power voltage is large
enough to cause a breakdown of Zener diode D6, D7 and D8, breakdown
current flows through resistor R31 into the base of output
transistor T1. Thus, the output transistor T1 is turned on and
absorbs the power surge voltage. The transistor T7 has a function
of quickly discharging a parasitic capacitance stored in the
vicinity of the junction diode D2. This makes it possible to
increase the cutoff speed of junction diode D2. In other words,
speedup in the cutoff operation of the junction diode D2 improves
the cutoff response of the output transistor T1.
In this forth embodiment, the junction diode D2 functions in the
same manner as those disclosed in the above-described first to
third embodiments. Furthermore, in an event of the breakdown of
Zener diodes D6, D7 and D8 due to a power surge voltage, the
junction diode D2 of the fourth embodiment prevents the breakdown
current from flowing into the transistor T7. Thus, the base
potential of the output transistor T1 is smoothly increased.
As described above, the fourth embodiment of the present invention
provides a load actuation circuit with a surge protection function
comprising: an output transistor (T1; emitter-follower transistor)
having a collector receiving a power voltage from a power line
(200) and an emitter connected to one end of a load (202) that is
grounded at the other end; a control circuit (103) controlling an
electric potential of a control electrode of the output transistor
(T1) to turn on or off the output transistor (T1); a feed circuit
(104) supplying current to the control electrode of the output
transistor (T1) from the power line (200) to turn on the output
transistor (T1) forcibly when any power surge voltage is superposed
on the power voltage of the power line (200); and a junction diode
(D2) preventing backward current flowing from the control electrode
of the output transistor (T1) to an output terminal of the control
circuit (103). Therefore, any power surge voltage can be surely
absorbed by the output transistor (T1).
According to the arrangement of the fourth embodiment, the junction
diode (D2) effectively prevents the backward current flowing from
the control electrode of the output transistor (T1) to an output
terminal of the control circuit (103). Therefore, the same effects
as those described in the first embodiment can be obtained.
Furthermore, according to the arrangement of the fourth embodiment,
the feed circuit (104) comprises a constant-voltage diode (D6, D7,
D8) and a current-limiting resistance element (R31) serially
connected between the power line (200) and the control electrode of
the output transistor (T1). This arrangement is advantageous in
that the circuit arrangement can be simplified. Moreover, a
high-speed charging for the output transistor can be realized.
Fifth Embodiment
A fifth embodiment will be explained with reference to FIG. 5. The
fifth embodiment is different from the first embodiment in the
arrangement of the surge detection circuit 101 and the first feed
circuit 104. More specifically, Zener diodes D3, D4 and D5 are
removed from the surge detection circuit 101. And, the transistor
T3 in the first feed circuit 104 is replaced by a schmitt trigger
circuit 205. Instead of using schmitt trigger circuit 205, a
comparator or a differential amplifier can be used as a comparable
component replaceable with the schmitt trigger circuit 205.
When a power surge voltage superposed on the power line 200 exceeds
a predetermined level, its divided voltage may exceed a reference
voltage of a high-level terminal of schmitt trigger circuit 205. In
such a case, the schmitt trigger circuit 205 generates a low-level
signal. In response to this low-level signal, the transistor T2 is
turned on and the output transistor T1 is turned on. Thereafter,
when the power surge voltage superposed on the power line 200 is
decreased, the divided voltage of the power surge voltage may fall
below the reference voltage of the high-level terminal of schmitt
trigger circuit 205. In this case, the schmitt trigger circuit 205
generates a high-level signal. In response to this high-level
signal, the transistor T2 is turned off and the output transistor
T1 is turned off.
According to the fifth embodiment, the output transistor T1 is
surely maintained at its on condition once the generation of a
power surge voltage is detected, until the power surge voltage is
sufficiently reduced. Hence, the performance for absorbing a power
surge voltage can be maintained adequately.
As this invention may be embodied in several forms without
departing from the spirit of essential characteristics thereof, the
present embodiments as described are therefore intended to be only
illustrative and not restrictive, since the scope of the invention
is defined by the appended claims rather than by the description
preceding them, and all changes that fall within the metes and
bounds of the claims, or equivalents of such metes and bounds, are
therefore intended to be embraced by the claims.
* * * * *